Particularly when weighing loads, e.g. of vehicles, there is a need for a device having a small thickness, onto which the load can be posed or the vehicle can be driven with one or a number of wheels; frequently the load must be applicable on a surface either off center or with any kind of distribution and in each such case the result of the measurement should not be affected by any errors.
It is well known that dynameters of various kinds are used to measure forces, e.g. devices with strain gauges, piezoelectric transducers or functioning with hydraulic principles.
A weighing device with the load resting on a liquid cushion is known from the FR-PS 71.22394. As a result of the pressure being equal everywhere in the cushion, the applied force is always fixed to the center of pressure of the cushion and it cannot be displaced off center.
An axle weighing scale with similar principle is known from U.S. Pat. No. 3,150,729. Here the load, which always acts in the same location, is equally carried and thereby measured by means of the pressure generated in a capsule. On the scale apparatus known from U.S. Pat. No. 3,752,245, the load is applied on to an elastic plate, which also rests on a liquid cushion. As the deflection of the plate changes according to the location where the force is applied, the resulting liquid pressure does not remain the same when the force acts off center.
Two similar weighing devices which are mounted on the pivot axis of a tractor truck or more generally between the load bearing structure of a vehicle and its axis, are known from U.S. Pat. No. 2,646,272 and U.S. Pat. No. 2,680,103. The load is transmitted onto an annular liquid chamber by an elastic plate and the resulting liquid pressure is measured. Here the correct functioning also depends on the load being applied symmetrically, because otherwise the resulting pressure will not remain the same.
U.S. Pat. No. 3,166,134 discloses a weighing device in which the load is carried by the pressure generated in a flexible liquid enclosure and is thereby measured. For the case when the load is applied off center, provision is taken for the total bearing surface of the liquid pressure to remain unchanged. As a result the pressure is proportional to the load.
The road-bearing meter according to U.S. Pat. No. 1,458,920 contains as gauge element a coil of thick walled tubing made of resilient material, which is filled with liquid. Upon loading the tubing, which acts as a progressive spring, is squeezed, whereby a liquid pressure is generated, which serves as the measurement signal. When the loadis applied off center, the liquid pressure cannot remain the same because the reduction of the open cross sectional area of the tubing is not proportional to the deforming force.